[Borek]

So why is this not assuming the reaction has gone to completion? Surely the reaction must reach completion to become basic?

No.

Look at the HH equation and think what will happen with pKa=7 acid

The stronger the acid, the earlier the solution becomes basic. To take extreme example - hydrocyanic acid, pKa = 9.31

0.01M solution has pH 5.65 - slightly acidic.

if you add 0.5% (!) of strong base, neutralizing 0.5% HCN, pH becomes 7.01

[mike]

Look at the HH equation and think what will happen with pKa=7 acid

The stronger the acid, the earlier the solution becomes basic. To take extreme example - hydrocyanic acid, pKa = 9.31

0.01M solution has pH 5.65 - slightly acidic.

if you add 0.5% (!) of strong base, neutralizing 0.5% HCN, pH becomes 7.01

Ah, sorry Borek I think we were talking about two different things, probably my fault, I do agree with what you have said but I was more refering to the way you would view the reaction equation when you are calculating the amount of base required for the neutralisation.

Cheers,